The following method is known as one of the methods for recovering ruthenium from solids containing ruthenium compounds: that is, the method comprises the steps of bringing such a solid into contact with a reducing gas at a high temperature to thereby reduce the ruthenium compound to obtain a metallic ruthenium; mixing the resultant solid which contains the metallic ruthenium with an oxidizing solution to thereby oxidize the metallic ruthenium; and dissolving the resultant ruthenium oxide (cf. Patent Documents 1 and 2)
Patent Document 1: JP-A-58-194745/1983
Patent Document 2: JP-A-2-197532/1990